Abstract
The determination of shear rate in column bioreactors is an important step to estimate the cell damage rate in shear-sensitive biosystems as well as for correlating hydrodynamic and mass transfer parameters. Due to the complexity of local shear rate measurement, it has been widely assumed that an average shear rate exists and is proportional to superficial gas velocity. The most serious shortcoming in the analysis of non-Newtonian behaviour in airlift reactors is the lack of a reliable method for determining a shear rate and an effective viscosity appropriate to the airlift geometry. Recently Shi et al. (Chem. Eng. Commun. 1990; 89: 22–35) presented an empirical correlation of effective shear rate as a function of superficial gas velocity and based on downcomer liquid circulation velocity. The external loop airlift reactor used by Shi et al. was 1.4 m in height, 0.194 m in riser diameter and 0.06 m in downcomer diameter. To validate the promising approach of Shi et al., this work has been carried out in a larger reactor of 6.5 m in height and 0.225 m in both riser and downcomer diameter. However, the rheological properties of the studied liquids and the superficial gas velocities were similar to those used by Shi et al.